Immediate post-training ICY administration of a synthetic peptide homologous to .beta.-A4, [Gln.sup.11 ].beta.-(1-28) [Asp Ala Glu Phe Arg His Asp Ser Gly Tyr Gln Val His His Gln Lys Leu Val Phe Phe Ala Glu Asp Val Gly Ser Asn Lys (SEQ ID NO: 1)] caused amnesia for FAAT in mice in dose-dependent fashion. Also amnestic were residues .beta.-(12-28) [Val His His Gln Lys Leu Val Phe Phe Ala Glu Asp Val Gly Ser Ash Lys (SEQ ID NO: 2)], .beta.-(18-28) [Val Phe Phe Ala Glu Asp Val Gly Ser Asn Lys (SEQ ID NO: 3)], and .beta.-(12-20) [Val His His Gln Lys Leu Val Phe Phe (SEQ ID NO: 4)] (1). These amnestic peptides have in common the tripeptidic sequence Val Phe Phe (SEQ ID NO: 5). Residue .beta.-(1-11) [Asp Ala Glu Phe Arg His Asp Ser Gly Tyr Gln (SEQ ID NO: 6)], which does not contain Val Phe Phe, was not amnestic (this study) FAAT experiments were performed with peptides containing the Val Phe Phe sequence from which was derived a topographic model for the binding site of amnestic peptides. Since the amnestic substances are memory-enhancing at lower concentration than those at which they cause amnesia, the model can be used to deduce the structure of potential memory-enhancing peptides and non-peptidic substances.